Surface water RO permeate remineralization through minerals recovery from brines

Abstract

Assisted-Reverse Electrodialysis (A-RED) technology was applied following reverse osmosis (RO) of a surface water resource in order to recover minerals from its brine and directly remineralize the RO unit's permeate. Four different sets of cation/anion exchange membranes were benchmarked using single- and mixed-salts synthetic solutions as well as real brine and permeate streams produced from three-stage reverse osmosis applied to Seine River water. The process, operating under equal permeate and brine channel flows (2 cm/s velocities) and applied voltage varying from 0 to 10 V, showed viable remineralization results. Optimal recovery at 10 V applied allowed increasing permeate mineral content from 20 mg/L CaCO3 up to values of 553 mg/L CaCO3 and from 100 μS/cm up to 1284 μS/cm for hardness and conductivity respectively. Tests using spiked micropollutants showed very low levels of micropollutant passage with over 98% rejection for 15 out of 18 compounds tested while natural organic matter (NOM) breakthrough was 2% on average (0.2 mg C/L).